Liquid crystal display apparatus and driving method thereof

ABSTRACT

This invention relates to a liquid crystal display device that minimizes picture quality deterioration caused by signal distortion. The present invention selects an area within an image, which has a rapidly increasing or decreasing gamma voltage, identifies a border delineating two different intensity regions within the area, computes an average intensity within the area, and weights the gamma voltage for each pixel within the area based on the average intensity. A liquid crystal display device according to the present invention includes: a liquid crystal display panel; an analyzer analyzing a brightness characteristic of data in an area within an image; an average video signal voltage generator calculating an average brightness value in the area; a bordering value processing part calculating a bordering brightness value in the area; and a weighting part adjusting a pixel voltage according to the average brightness value and the bordering brightness value.

This application claims the benefit of the Korean Patent Application No.P2004-96630 filed on Nov. 23, 2004, which is hereby incorporated byreference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid crystal display devices forminimizing picture quality deterioration caused by signal distortion.

2. Description of the Related Art

Generally, a liquid crystal display device controls the lighttransmittance of a liquid crystal by use of electric fields, therebydisplaying a picture.

FIG. 1 is a diagram representing a liquid crystal display device of therelated art. Referring to FIG. 1, the related art liquid crystal displaydevice includes a liquid crystal display panel 1; a plurality of datatape carrier packages (TCP) 8, which are connected between the liquidcrystal display panel 1 and data printed circuit boards (PCB) 12; aplurality of gate TCPs 14A to 14D connected to another side of theliquid crystal display panel 1; data driver integrated circuits (IC) 10mounted on each of the data TCPs 8; and gate drive ICs 16A to 16Dmounted on each of the gate TCPs 14A to 14D.

The liquid crystal display panel 1 includes a lower substrate 2 where athin film transistor array is formed together with various signal lines;an upper substrate 4 where a color filter array is formed; and a liquidcrystal, which is injected between the lower substrate 2 and the uppersubstrate 4. The liquid crystal display panel 1 includes a picturedisplay area 21, wherein the picture display area 21 includes liquidcrystal cells that are defined by the crossing of the gate lines 20 andthe data lines 18. Data pads extend from the data line 18, and gate padsextend from the gate line 20, in the outer area of the lower substrate 2located at an outer part of the picture display area 21.

The data TCP 8 has the data drive IC 10 mounted on it and input pads 24and output pads 25 electrically connected to the data driver IC 10. Theinput pads 24 of the data TCP 8 are electrically connected to the outputpads 25 of a data PCB 12 through an anisotropic conductive film(hereinafter “ACF”), and the output pads 25 are electrically connectedto the data pads on the lower substrate 2 through the ACF.

The data driver ICs 10 convert a digital pixel data signal into ananalog pixel voltage signal and supply the analog pixel signal to thecorresponding data line 18 on the liquid crystal display panel 1.

The gate TCP 14A to 14D respectively have gate driver ICs 16A to 16Dmounted on them, a gate drive signal transmission line group 28, and theoutput pads formed to connected to the gate driver ICs 16A to 16D. Thegate driver signal transmission line group 28 is electrically connectedto the signal line group 26 on the lower substrate 2 through the ACF,and the output pads 30 are electrically connected to the gate pads onthe lower substrate 2 through the ACF.

The gate driver ICs 16A to 16D sequentially supply a scanning signal,i.e., gate high voltage signal VGH, to the gate lines 20 in response toinput control signals. The gate driver ICs 16A to 16D supply a gate lowvoltage signal VGL to the gate lines in the remaining period except fora period when the gate high voltage signal VGH is supplied.

The signal line group 26 generally includes the following: signal linesthat supply DC voltage signals like the gate high voltage signal VGH;the gate low voltage signal VGL; a common voltage signal Vcom; a groundvoltage signal GND and a power supply voltage signal VCC that aresupplied from a power supply; and gate control signals like a gate startpulse GSP, a gate shift clock signal GSC and a gate output enable signalGOE, which are supplied from a timing controller.

The signal line group 26 of the related art liquid crystal displaydevice is formed in a minute parallel pattern in a very limited narrowspace, such as the pad area, which is located at the outer area of thepicture display part 2l. The signal line group 26 is formed of the samegate metal layer as the gate lines 20. The gate metal is generally ametal that has a relatively high specific resistance 0.046, like AlNd.In this way, the signal line group 26 is formed in a minute pattern in alimited area and of a gate metal which has the relatively high specificresistance. Accordingly, the signal line group 26 includes a relativelyhigh line resistance component X in comparison with the signal linesformed of a copper thin film in the existing gate PCB. Further, the ACF(not shown) for connecting the signal line group 26 to the gate drivesignal transmission line group 28 includes a designated connectionresistance component Y. In addition, the gate driver signal transmissionline group 28 formed on a chip-on-film (COF), or the gate TCP 14A to14D, include a designated line resistance component Z. These resistancecomponents have a difference as much as X+2Y+2Z between the adjacentICs. The resistance components cause line resistance to increase withincreasing distance from the data PCB 12, thereby attenuating the signalsupplied through the signal line group 26. Especially, the commonvoltage Vcom signal which is the standard of the gate drive signals isdistorted by such a resistance, thereby deteriorating the quality of apicture which is displayed in the picture display part 2 1.

The signal line group 26 has line resistances (a, b, c, d) proportionalto its line length, and is connected in series through the first andfourth gate TCPs 14A to 14D. The common voltage Vcom supplied to eachgate driver IC 16A to 16D is changed by the line resistances (a, b, c,d) of the signal line group 26. Accordingly, the first to fourth commonvoltages VCOM1 to VCOM4 have a relationship such thatVCOM1>VCOM>VCOM3>VCOM4. Accordingly, a difference in brightness occursbetween horizontal line blocks A to D, which are respectively connectedto the gate driver ICs 16A to 16D. The brightness difference of thehorizontal line block A to D is shown in a horizontal line 32 phenomenonto make a screen appear to be divided, thereby resulting in a cross-talkphenomenon caused by the resistance between lines as well as a picturequality deterioration.

FIG. 2 illustrates a vertical stripe pattern, which is a test patternwhereby the distortion of the common voltage Vcom is most intenselygenerated. Herein, an equivalent circuit between a panel and a drivecircuit can be expressed as illustrated in FIG. 3.

Referring to FIG. 3, the related art cross-talk phenomenon results froman alternating current lac, which is imparted to the resistor R_ITO ofthe common electrode by energy that is stored in capacitors Cb and Cg,which are between a black pixel V_B and a gray pixel V_G The alternatingcurrent lac forms a path which is connected to a third node Vc and agamma resistor R_gamma through a pad resistor R_pad that makes thedriver IC in contact with the panel. A horizontal cross-talk isgenerated in a bordering part of a black bar due to a voltage couplingresulting from a difference between the voltage of the common electrodeof a second node Vb and a gamma voltage of the third node Vc.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay apparatus and driving method thereof that substantially obviatesone or more of the problems due to limitations and disadvantages of therelated art.

An advantage of the present invention is that it minimizes picturequality deterioration caused by signal distortion.

Another advantage of the present invention is that it minimizes theeffect of gate line voltage changes due to signal line resistance.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and described, a liquid crystaldisplay device includes a liquid crystal display panel; an analyzer thatanalyzes a brightness characteristic of data in an area within an image;an average video signal voltage generator that calculates an averagebrightness value in the area; a bordering value processing partcalculates a bordering brightness value in the area; and a weightingpart that adjusts a pixel voltage according to the average brightnessvalue and the bordering brightness value.

In another aspect of the present invention, a method of driving a liquidcrystal display device includes analyzing a brightness characteristic ofdata in an area within an image; detecting a border in the area on thebasis of the brightness characteristic of the data; calculating anaverage value in the area; and weighting a pixel data value according tothe average value and a gamma voltage corresponding to the border in thearea.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a plane view illustrating a configuration of a related artliquid crystal display device;

FIG. 2 is a diagram representing a test pattern in which a commonvoltage distortion can be observed;

FIG. 3 is a diagram representing an equivalent circuit between a paneland a drive circuit in the liquid crystal display device illustrated inFIG. 1;

FIG. 4 is a diagram representing a liquid crystal display deviceaccording to an embodiment of the present invention;

FIG. 5 illustrates a liquid crystal display panel of FIG. 4;

FIG. 6 is a diagram representing an equivalent circuit between a paneland a drive circuit of FIG. 5; and

FIG. 7 is a block diagram representing a driving method of the liquidcrystal display device according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to an embodiment of the presentinvention, example of which is illustrated in the accompanying drawings.

FIG. 4 is a diagram representing a liquid crystal display deviceaccording to an embodiment of the present invention. Referring to FIG.4, the liquid crystal display device according to the present inventionincludes a liquid crystal display panel 122 in which liquid crystalcells are arranged in a matrix pattern; and a driver device 121 fordriving the liquid crystal display panel 122.

Referring to FIG. 5, the liquid crystal display panel 122 includes acolor filter array substrate 81 and a thin film transistor arraysubstrate 91 which are bonded with a liquid crystal Clc between them.The liquid crystal Clc rotates in response to an applied electric field,thereby controlling the transmittance of the light that is incidentthrough the thin film transistor array substrate 91.

The color filter array substrate 81 includes a black matrix (not shown),a color filter 82 and a common electrode 84, which are formed on therear surface of an upper substrate 80A. The black matrix is formed of anopaque material to absorb the light which is incident from the adjacentcell, thereby preventing the deterioration of contrast. The color filter82 has color filter layers of red R, green G, blue B disposed in astripe shape to transmit a light of a specific wavelength range, therebyenabling color display.

The thin film transistor array substrate 91 is formed on the frontsurface of a lower substrate 80B. The thin film transistor arraysubstrate 91 includes data lines DL and gate lines GL that cross eachother, and a TFT formed at the crossing. The TFT includes a gateelectrode connected to the gate line GL, a source electrode connected tothe data line DL, and a drain electrode facing the source electrode witha channel between them. The TFT is connected to a pixel electrode 92through a contact hole that enables contact with the drain electrode.The TFT selectively supplies a data signal from the data line DL to thepixel electrode 92 in response to the gate signal from the gate line GL.

The pixel electrode 92 is located at a cell area, which is defined bythe data line DL and the gate line GL. The pixel electrode 92 is formedof a transparent conductive material with a high light transmittance.The pixel electrode 92 generates a potential difference with the commonelectrode 84 formed on the upper substrate 80A, according to the datasignal supplied through the drain electrode. The potential differencecauses the liquid crystal Clc located between the lower substrate 80Band the upper substrate 80A to rotate due to the liquid crystal'sdielectric anisotropy. Accordingly, the light supplied through the pixelelectrode 92 from the light source is transmitted to the upper substrate80A, depending on the strength of the electric field.

The driver device 121 includes: a gate driver 126 for driving the gatelines GL; a data driver 124 for driving the data lines DL; a gammavoltage supplier 128 to supply a gamma voltage to the data driver 124; atiming controller 120 for controlling the gate driver 126, the datadriver 124, and the gamma voltage supplier 128; and an average videosignal voltage generator 150 for calculating an average video signalbased on a histogram analysis of a specific area.

The timing controller 120 controls the timing of the gate driver 126 andthe data driver 124 and supplies the pixel data signal to the datadriver 124.

The gate driver 126 sequentially supplies a scanning signal to the gatelines GL and sequentially drives the liquid crystal cells on the liquidcrystal display panel 122 one line at a time.

The data driver 124 supplies the pixel voltage signal to each of thedata lines DL corresponding to the scanning signal supplied to any oneof the gate lines GL. Accordingly, the liquid crystal display devicecontrols light transmittance by an electric field applied between thepixel electrode 92 and the common electrode 84 in accordance with thepixel voltage signal for each liquid crystal cell, thereby displaying apicture.

The average video signal voltage generator 150 generates and analyzes ahistogram of an area where the gamma voltage rapidly changes andcalculates an average value by use of a histogram averaging method togenerate a voltage corresponding to the average gamma value.

An exemplary equivalent circuit 160 between a liquid crystal displaypanel 122 and a driver device 121 is illustrated in FIG. 6. Referring toFIGS. 4 and 6, the equivalent circuit 160 includes: a data line DLresistor Rs1, a pixel capacitor Cs1 and a common electrode resistor Rgwhich are connected in series between the common voltage Vcom and a datasignal voltage Vs1 that is supplied from the data driver 124; a firstnode N1 between a common electrode resistor Rg and the pixel capacitorCs1; a data line DL resistor Rs2 and a pixel average capacitor Cs whichare connected in series between the first node N1 and the average videosignal voltage Vs that is supplied from the average video signal voltagegenerator 150; and a data line DL resistor, a TFT conductive resistor Raand a liquid crystal Clc which are connected in series between the gammavoltage Va and the first node N1.

A driving method between the panel and the drive device according to thepresent invention is explained in reference to the block diagramillustrated in FIG. 7.

Referring to FIG. 7, an exemplary driving method, as implemented by thedriver device 121 according to the present invention, is as follows.Each block within FIG. 7 may represent a software component running onone or more embedded processors or microcontrollers. The window 162collects a block of data, referred to as a set area, within the imagewhere the gamma voltage Va of the pixel capacitor Ca has either rapidlyincreased of decreased. The histogram analyzer 164 generates a histogramof the set area. In doing so, the histogram analyzer 164 generates anarray of values corresponding to the gray level and its frequency ofoccurrence within the set area. The histogram analyzer 164 thendetermines the amount of increase or decrease in gamma voltage Va bydividing the set area into black, gray and white colors, eachcorresponding to a histogram bin, and calculating an average brightnessvalue corresponding to each of the three sections by use of thehistogram averaging method. The result of the histogram analyzer 164 isthen supplied to a bordering value processing part 166 as well as theaverage video signal voltage generator 150.

The average video signal generator 150 takes the averaged histogram binvalues from histogram analyzer 164 and generates an offset to shiftaverage gray level to compensate for a lopsided gray level distribution.The output of average video signal generator 150, which includes thegray level offset, is applied to the input of switch 167.

The bordering value processing part 166 detects a border within the setarea, such as a horizontal line 32 between regions A and B in FIG. 1. Indoing so, the bordering value processing part 166 may compare thehistogram data provided by histogram analyzer 164 with a pre-setreference value or a reference histogram. The bordering value processingpart 166 then selectively applies the signal generated from the averagevideo signal voltage generator 150 to the weighting part 168 by use of aswitch 167. For example, bordering value processing part 166 may comparethe average gray value i (from the average brighness values computed byhistogram analyzer 164) with two threshold values. Particularly, for apossible brightness value ranging between 0 and 255, bordering valueprocessing part 166 may determine if i conforms to the either of thefollowing logical conditions: 0<i<64, or 200<i<255. If either of theseconditions are true, then bordering value processing part outputs a highlogical value (e.g., binary “1”), which it sends to the gate of switch167. If either of the above logical conditions are true, then the graylevel distribution is sufficiently lopsided to correspond to horizontalcrosstalk.

If bordering value processing part 166 detects a lopsided gray leveldistribution, it outputs a high logic level to switch 167, which in turnapplies the gray level offset generated by average video signal voltagegenerator 150 (and applied to input of switch 167) to weighting part168. Weighting part 168 applies the offset to the gamma voltage fromgamma voltage supplier 128 to offset the lopsided gray leveldistribution of border areas within the set area. The corrected signal,which is the output of weighing part 168, is applied to a pertinentpixel line to minimize horizontal cross-talk.

As described above, the liquid crystal display device according to thepresent invention analyzes a histogram of the area where the change ofthe video signal is high to generate the average video signal voltageand supplies the average video signal voltage to the area, therebyminimizing horizontal cross-talk. Accordingly, the liquid crystaldisplay device according to the present invention can improve picturequality.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A liquid crystal display device, comprising: a liquid crystal displaypanel; an analyzer that analyzes a brightness characteristic of data inan area within an image; an average video signal voltage generator thatcalculates an average brightness value in the area; a bordering valueprocessing part that calculates a bordering brightness value in thearea; and a weighting part that adjusts a pixel voltage according to theaverage brightness value and the bordering brightness value.
 2. Theliquid crystal display device according to claim 1, further comprising:a switch connected between the average video signal voltage generatorand the weighting part.
 3. The liquid crystal display device accordingto claim 2, wherein an output of the analyzer controls the switch. 4.The liquid crystal display device according to claim 1, furthercomprising a gamma voltage supplier that generates a gamma voltagecorresponding to the data, wherein the gamma voltage supplier isconnected to an input of the weighting part.
 5. A method of driving aliquid crystal display device, comprising: analyzing a brightnesscharacteristic of data in an area within an image; detecting a border inthe area on the basis of the brightness characteristic of the data;calculating an average value in the area; and weighting a pixel datavalue according to the average value and a gamma voltage correspondingto the border in the area.
 6. The method according to claim 5, whereinanalyzing the brightness characteristic includes generating a histogramof the data.
 7. The method according to claim 6, wherein detecting theborder includes comparing the histogram of the data with a referencehistogram.